1. Field of the Invention
The present invention relates to an image forming apparatus using an electrophotography system, such as a color printer, and in particular, an image forming apparatus, such as an ultrahigh-speed continuous paper color printer capable of forming a full color image on continuous paper as a recording medium at an ultrahigh speed.
2. Description of the Related Art
Such a printer has been known as the printer of this kind that toner images of colors including yellow (Y), magenta (M), cyan (C) and black (K) are multiply transferred directly to paper from photoreceptor drums forming the toner images to form a full color image without an intermediate transfer medium used. In the printer, the toner images of the colors are transferred from the photoreceptor drums directly to paper without an intermediate transfer medium used, whereby the running cost due to consumption of the intermediate transfer medium is prevented from being increased.
For example, as shown in FIG. 7, an ultrahigh-speed continuous paper color printer 100 has image forming parts 101Y, 101M, 101C and 101K corresponding to colors of yellow (Y), magenta (M), cyan (C) and black (K), respectively, arranged in series, in which toner images formed with photoreceptor drums 102 of the image forming parts 101Y, 101M, 101C and 101K are multiply transferred directly to continuous paper 103 fed at an ultrahigh speed, and then fixed with a fixing part 104 employing a flash fixing system, so as to form a full color image.
In the ultrahigh-speed continuous paper color printer, a mark 105 for detecting color registration is formed on a part of the paper 103 for precisely controlling the positions of the images (registration) formed with the image forming parts 101Y, 101M, 101C and 101K corresponding to colors of yellow (Y), magenta (M), cyan (C) and black (K), respectively, and the mark 105 for detecting color registration is detected with a color registration sensor 106 to calculate registration deviation amounts of the images of respective colors, which are fed back to the paper feed amount and the drawing positions in main scanning direction and subscanning direction in the image forming parts 1O1Y, 101M, 1O1C and 101K.
However, the aforementioned conventional technique includes the following problems. In the conventional ultrahigh-speed continuous paper color printer as shown in FIG. 8, it is necessary that a mark 105 for detecting color registration is formed on a part of paper 103 for precisely controlling the color registration, and therefore, the mark 105 for detecting color registration remains on the paper 104.
Accordingly, it is necessary in the conventional ultrahigh-speed continuous paper color printer that the mark 105 for detecting color registration is cut out in the final stage, or in alternative, a user is asked to tolerate the mark 105 for detecting color registration remaining on the paper 103. Therefore, there is such a problem that the constitution of the printer becomes complicated, or the disadvantage of the mark 105 for detecting color registration remaining on the paper 104 is rendered to a user.
As a technique for providing a color image with high quality by preventing color registration deviation, JP-A-2001-142280 proposes an image forming apparatus. However, the image forming apparatus proposed in JP-A-2001-142280 has a transfer medium including an intermediate transfer belt and a cleaning unit for cleaning the transfer medium, and thus the configuration, on which the apparatus is based, is different from the invention.